https://marketplace.tf/items/tf2/30876;5;u3026 - Sales at $5 (2.8 Keys), $5.95 x4 (3.35, 3.35, 3.4, and 3.45 Keys), $4.3 (2.5 Keys), and $5.89 (3.5 Keys)

https://backpack.tf/item/8176887046 - Either the 2/25 or 2/27 sale

https://backpack.tf/item/6253519322 - Either the 2/25 or 2/27 sale

https://backpack.tf/item/6252973933 or https://backpack.tf/item/6268619504 - 1/16 sale

https://backpack.tf/profiles/76561198097271466#!/compare/1584316800/1584403200 - Sold for 3 Keys

https://backpack.tf/profiles/76561198850274253#!/compare/1581120000/1581206400 - Sold for 3 Keys

https://backpack.tf/profiles/76561198010068578#!/compare/1581206400/1581379200 - Sold for 3 Keys

https://backpack.tf/profiles/76561198074410092#!/compare/1581379200/1581465600 - Strange Starboard Crusader + 1 Key (high)

https://backpack.tf/profiles/76561198928421771#!/compare/1580342400/1580428800 - Sold for 5 Keys (high)

https://imgur.com/a/kqiDDbZ - 2 Sellers at 3.55 Keys (1 is new, 1 has been listed since 3/9)

http://webcache.googleusercontent.com/search?q=cache:CLzVPokm9qAJ:https://marketplace.tf/items/tf2/30876;5;u3026&hl=en&gl=us&strip=1&vwsrc=0

https://backpack.tf/item/6976670063

https://backpack.tf/item/6341053969

https://imgur.com/a/nM0bzq7 - Unbumped 4 day seller at 4 Keys and a seller at 5 Keys (also listed since 3/9 in the picture above)

https://backpack.tf/item/6252814679

https://backpack.tf/item/6781262415

When calculating the Marketplace sales, you don't need to factor the fee in. We're looking explicitly at the price the item sells for.

I would go 2.8 - 3.5 Keys here, cutting off 2.5 (barely above buyers) and 5.